Flame-resistant polyurethane compositions

ABSTRACT

Novel polyurethane foams possessing improved resistance to burning and flame propagation are prepared by employing 2,5tolylene diisocyanate or its ring-substituted chloro- or bromoderivatives as a portion of the isocyanate component used in preparing the polyurethane foams.

United States Patent Franke et al.

[151 3,684,753 Aug. 15, 1972 [54] FLAME-RESISTANT POLYURETHANECOMPOSITIONS [72] Inventors: Norman W. Franke, Penn Hills Twsp.,Allegheny County; Gary M.

Singerman, Borough of Monroeville, both of Pa.

[73] Assignee: Gulf Research &Development Company, Pittsburgh, Pa.

[22] Filed: Feb. 22, 1971 [2]] Appl. No.: 117,749

52 us. (:1. ..'260/2.5 AT, 252/182, 260/25 AJ, 260/75 NT, 260/775 AT 511111. Cl. ..C08g 22/18, C08g 22/44 581 Field of Search.....260/2.5 AT,77.5 AT, 75 NT, 260/453 AR; 252/182 [56] References Cited UNITED STATESPATENTS 3,488,374 l/ 1970 Kober ..260/2.5 AT

FOREIGN PATENTS OR APPLICATIONS 1,158,562 7/1969 Great Britain OTHERPUBLICATIONS Kunststoff l-landbuch, Band Vll, Vieweg und Hochtlen, CarlHanser Verlag; Munich 1966, page 16 Primary Examiner-James A. SeidleckAssistant Exdminer-C. Warren l-vy Att0meyMe yer Neishloss, Deane E.Keith and Donald L. Rose ABSTRACT 5 Claims, No Drawings Polyurethane, 4

FLAME-RESISTANT POLYURETHANE COMPOSITIONS This invention relates topolyurethanes and their preparation. More particularly, the inventionrelates to novel polyurethane foams possessing improved resistance toburning and flame propagation which may be prepared by the use of, aspart of the isocyanate component, 2,5-tolylene diisocyanate, itsringhalogenated derivatives or mixtures thereof.

Polyurethane foams have found wide and varied use in industry. Forexample, rigid foams are used as heat insulators, and semirigid andflexible foams are used in cushioning, shock absorption, and packagingapplications. In many of these important areas, it is required that thematerial be fire-retardant. Unfortunately, the highly flammable natureof most conventional polyurethane foams limits their acceptance in manyapplications. This is especially true of foams which are based wholly orpartly on the usual commercial mixtures of 2,4- and 2,6-tolylenediisocyanate. Such foams burn rapidly and support combustion onceignited.

The use of certain additives for the purpose of reducingthe flammabilityof polyurethane materials and polyurethane foams is well known to thoseskilled in the art. Among the additives currently employed for such useare various types of phosphorus-containing compounds. The phosphoruscompounds are generally used either alone or in combination with othermaterials such as organic or inorganic compounds of antimony orhalogenated organic materials. The phosphorus-containing compounds maybe non-reactive chemicals such as tris(2-chloroethyl)phosphate,tris(2,3-dibromopropyl)phosphate, ammonium phosphate, or morecomplicated hydroxy compounds which are reacted into the foam structure.Antimony trioxide is also used to reduce the flammability of urethanes,especially in combination with other materials such as a halogenatedhydrocarbon or ammonium phosphate.

One drawback of these known compounds and combinations of compounds,however, has been the fact that generally large amounts (up to 35percent) of the additive must be incorporated into the urethane polymerin order to render it acceptably flame resistant. Such large quantitiesof additives often have a deleterious effect upon the physical andmechanical properties of the foam, such as dimensional stability,compression strength, density and the like. Mineral fillers tend tosettle out; foams are weakened and show a tendency to shrink; someadditives tend to crystallize or oil out of the polymer (plasticizermigration) after a relatively short time of incorporation therein, thusrestoring the foam to its original untreated condition.

Much of the polyurethane foam currently produced is foam in which theisocyanate component is either wholly 2,4- and/or 2,6-tolylenediisocyanate (usually an 80/20 or 65/35 blend of 2,4-/2,6-tolylenediisocyanate) or a blend of 2,4- and 2,6-tolylene diisocyanate with oneor more polyisocyanates which are not homologs of tolylene diisocyanate,such as polymethylene polyphenylisocyanate or 4,4'-diphenylmethanediisocyanate and the like as exemplified hereinbelow. The expressionpolyisocyanate, as used herein, is intended to include diisocyanate.

We have now made the surprising discovery that such foams, whetherrigid, semirigid, or flexible, which are based entirely or partly ontolylene diisocyanate, possess improved resistance to burning and flamepropagation if part of the 2,4- and 2,6-tolylene diisocyanate blendnormally employed is replaced with 2,5- tolylene diisocyanate. The 2,4-and 2,6-isomers of tolylene diisocyanate are meta-diisocyanates, whereas2,5-tolylene diisocyanate is a para-diisocyanate. It is surprising andunexpected that a change in the orientation of the two isocyanate groupson the benzene ring from a meta to a para orientation would result in adecrease in the flammability of polyurethane foams. This improvedresistance to burning and flame propagation occurs both in the absenceof and in the presence of flammability retarding additives and when suchadditives are used, suitable flame retardance is obtained atsubstantially lower concentrations of such additives. The 2,5-tolylenediisocyanate is not regarded herein as a flame-retarding additive butrather is one of the reacting monomers whose presence in the polymerchains enhances the flame retardancy and resistance to burning of thefinal foamed polymer.

It is therefore an object of the invention to produce novel polyurethanefoams possessing improved resistance to burning and flame propagation.

It is a further object of the invention to provide novel polyurethanefoams possessing improved resistance to burning and flame propagationwithout the use of flame-retarding additives.

It is another object of the invention to provide polyurethane foamshaving good resistance to burning and flame propagation using loweramounts of flame-retarding additives than heretofore used with aresulting improvement in the chemical and physical properties of thepolyurethane foams.

These objects, and other objects which will be apparent by reading themore detailed description hereinbelow, are achieved by replacing aportion of the isocyanate component conventionally employed in theproduction of polyurethane foams, particularly 2,4- and/or 2,6-tolylenediisocyanate, by 2,5-tolylene diisocyanate, its mono-, diand tri-,ring-halogenated derivatives, or mixtures thereof. Advantageously, theamount of 2,5-tolylene diisocyanate or its halogenated derivatives whichare employed according to the process of the invention is from about 8weight percent to about 60 weight percent, preferably 15 percent to 50percent, of the total isocyanates used in making the polyurethanes,whether the isocyanates used are solely of the tolylene diisocyanatetype or other polyisocyanates which are not homologs of tolylenediisocyanate or mixtures of these. Such non-homologous polyisocyanatesare exemplified hereinbelow. Since the incorporation of 2,5-tolylenediisocyanate in the polyurethane foam composition tends to reduce thevalues of several ASTM tests such as the indentation load deflectiontest, the compression load deflection test, the percent compression settest and the indentation residual gage load test, the amount of2,5-tolylene diisocyanate in the total isocyanates has been restrictedto a maximum value of about 60 percent in order to avoid the unduelowering of the properties indicated by these tests while benefittingfrom the advantages from the use of 2,5-tolylene diisocyanate.

The principal reactants employed in the preparation of polyurethanefoams are an active-hydrogen containing compound such as a polyhydroxypolyether and an organic polyisocyanate. Rigid polyurethane foams aregenerally provided by employing a polyhydroxy polyether having ahydroxyl number between about 175 and 800 as the active-hydrogencontaining compound. In preparing semirigid foams the hydroxyl number ofthe polyhydroxy polyether should be between about 75 and about 175,while flexible foams are provided by employing polyhydroxy polyethershaving hydroxyl numbers between about 30 and about 60 In the preparationof polyurethanes according to the invention, conventional procedures areemployed. The various methods for the preparation of polyurethane foamsare well known in the art and do not require detailed discussion; see,for example, Dombrow, Polyurethanes, Reinhold Publishing Corp., NewYork, pages 1 to 105 (1957); Saunders et al., Polyurethanes, Part I,Interscience Publishers, N. Y. (1962).

One of the commonest procedures consists in reacting a polyol, forexample, a polyester or polyether, with an organic polyisocyanate andwith water, if necessary in the presence of catalysts, surface activeagents or other auxiliary agents, whereby simultaneous interactionbetween the isocyanate, water and the polyol occurs to give the requiredfoam product. This is the socalled one-shot procedure. Alternatively thepolyol may be reacted with sufficient polyisocyanate to give anintennediate reaction product containing free isocyanate groups and thisproduct, known as prepolymer, may then be reacted with water, if desiredin the presence of catalyst, surface active agents or other auxiliaryagents, in order to produce the final foamed product. This latter is theso-called prepolymer process. Many variations in the method of carryingout these basic processes are known.

Any of the widely known organic polyisocyanates, in accordance with thepresent invention, can be used in admixture with 2,5-toly1enediisocyanate, its halogenated derivates, or mixtures thereof. Typicalexemplificative isocyanates include, but are not limited to, thefollowing: 2,4-tolylene diisocyanate; 2,6- tolylene diisocyanate;methylene-bis(4-phenyl isocyanate 3 ,3 'bitoluene-4,4 '-diisocyanate; 3,3 dimethoxy-4,4'-biphenylene diisocyanate;naphthalene-1,S-diisocyanate; hexamethylene diisocyanate; 1,4-phenylenediisocyanate; polyphenylene polymethylene polyisocyanate; mixtures ofthese; and the like. The amount of isocyanate employed in thepreparation of the polyurethane foams should be sufiicient to provide atleast 0.7 NCO group per hydroxyl group present in the reaction system.An excess of isocyanate compound may be conveniently employed, however,this is generally undesirable due to the high cost of the isocyanatecompounds. It is preferable, therefore, to employ no greater than about1.5 NCO groups per hydroxyl group and preferably between about 0.9 and1.1 NCO groups per hydroxyl group.

Any of the polyols conventionally employed in the preparation ofpolyurethane foams can be employed in the process of the invention. Thepolyol component can be a single polyol compound or it can be a mixtureof two or more polyol compounds. It is preferred to use a polyol havingfrom two to eight hydroxyl groups and a molecular weight of from about200 to about 5,000. The most suitable compounds are prepared by reactingan alkylene oxide such as, ethylene oxide, 1,2 propylene oxide,1,2-butylene oxide, 2,3-butylene oxide, epichlorohydrin, styrene oxide,or the like with an active hydrogen containing component whichpreferably has at least three hydrogen atoms which can be reacted withthe alkylene oxide to add the alkylene oxide onto the molecule and thusproduce a polyhydric polyalkylene ether. The most suitable compounds ofthe latter type are either polyamines or polyhydric alcohols includingfor example, ethylene diamine, 2,4- diamino toluene, 1,3-propylenediamine, 4,4- diaminodiphenyl methane, p-phenylene diamine, 1,4- butanediamine, 1,6-hexarnethylene diamine, trimethylolpropane, glycerine,pentaerythritol, sorbitol, 1,2,6-hexane triol, mannitol,alpha-methyl-d-glucoside and the like. It is also possible to use thoseactive hydrogen compounds which are substantially difunctional such as,for example, polyethylene glycol having a molecular weight of 1,500,polypropylene glycol having a molecular weight of 2,000 and similardifunctional components which normally produce flexible, foamedpolyurethanes when reacted with organic diisocyanates.

It is also possible to use polyesters as the active hydrogen containingcompound. For this purpose, any suitable polyester can be used such asare obtained, for example, from polycarboxylic acids and polyhydricalcohols. Any suitable polycarboxylic acid can be used such as, forexample, oxalic acid, malonic acid, succinic acid, glutaric acid, adipicacid, pimelic acid, suberic acid, azelic acid, sebacic acid, brassylicacid, thapsic acid, maleic acid, fumaric acid, glutaconic acid,alpha-hydromuconic acid, beta-hydromuconic acid,alpha-butyl-alpha-ethylglutaric acid, alpha-beta diethylsuccinic acid,isophthalic acid, terephthalic acid, hemimellitic acid, trimelliticacid, trimesic acid, mellophanic acid, prehnitic acid, pyromelliticacid, benzenepentacarboxylic acid, 1,4-cyclohexanedicarboxylic acid,3,4,9,10-perylenetetracarboxylic acid and the like. Any suitablepolyhydric alcohol can be used such as, for example, ethylene glycol,1,3-propy1ene glycol, 1,2-propylene glycol, 1,4-butylene glycol, 1,3-butylene glycol, 1,2-butylene glycol, 1,5-pentane diol, 1,4-pentanediol, 1,3-pentane diol, 1,6-hexane diol, 1,7-heptane diol, glycerine,trimethylol propane, 1,3,6- hexanetriol, triethanolamine,pentaerythritol, sorbitol and the like.

The polyol component employed in making polyurethanes in accordance withthis invention can, if desired, also include a phosphorus-containingpolyol of the type known in the art to impart fire retardancy topolyurethanes. In this way it is possible to enhance still further thedegree of fire retardancy imparted to the resulting polyurethanes by2,5-tolylene diisocyanate, and its halogenated derivatives. Less ofthese phosphorus-containing polyols may be used to impart the desireddegree of fire retardancy to the polyurethanes than was hithertopossible, resulting in lower costs and in lesser adverse effects uponphysical properties such as dimensional stability which can be caused bythe amounts of the phosphorus-containing polyols currently employedcommercially.

Examples of phosphorus-containing polyols which can be employed incombination with the above polyols are dialkylN,N-di(hydroxyalkyl)aminomethane phosphonates such as diethyl N,N-di(2-hydroxyethyl)aminomethane phosphonate, propylene oxide adducts ofphosphoric acid such as those described in U.S. Pat. Nos. 2,372,244 and3,094,549, and tris propylene glycol phosphates such as those describedin U.S. Pat. No. 3,061,625.

The foaming agent employed may be any of those known to be useful forthis purpose, such as water, the halogenated hydrocarbons, and mixturesthereof. Typical halogenated hydrocarbons include, but are not limitedto, the following: monofluorotrichloromethane; difluorodichloromethane;1 1 ,2-trichloro-1 ,2,2- trifluoroethane; methylene chloride; chloroformand carbon tetrachloride. The amount of foaming agent employed may bevaried within a wide range depending on the desired density of theresulting foam. Generally, however, the halogenated hydrocarbons areemployed in an amount from 1 to 50 parts by weight per 100 parts byweight of the polyhydroxy polyether and water can be employed in anamount of from 0.1 to parts by weight per 100 parts by weight of thepolyhydroxy polyether.

Any of the catalysts known to be useful in the preparation ofpolyurethane foams can be employed in this process including tertiaryamines, metallic salts and mixtures thereof. Typical tertiary aminesinclude, but are not limited to, the following:1,1,3,3-tetramethylbutanediamine, 1,3-bis(dimethylamino)-2-propanol, N-methyl morpholine, N-hydroxyethyl morpholine, triethylene diamine,triethylamine and trimethylamine.

Typical metallic salts include, for example, the salts of antimony, tinand iron, e.g., dibutyl tin dilaurate, stannous octoate, etc. Generallyspeaking, the catalyst is employed in an amount from 0.1 to 2.0 percentby weight based on the polyhydroxy polyether.

It is very desirable to have a foam stabilizer or surfactant present inthe course of the reaction, and here one can use organosilicone polymersincluding polydimethyl siloxane and preferably one having a viscositybetween about 20 and about 200 centipoises at 25 C. or an alkyl silanepolysiloxane polyoxyalkylene block copolymer such as those disclosed inU.S. Pat. No. 2,834,748. Other surfactants such as ethylene oxidemodified sorbitan monopalmitate, ethylene oxide modifiedpolypropyleneether glycol, sulphonated castor oil, and oxyethylated talloils can be used.

Various additives can be employed which serve to modify properties orlower cost such as fillers including clay, calcium sulfate, or ammoniumphosphate. lngredients such as dyes may be added for color, and fibrousglass, asbestos, or synthetic fibers can be added for strength. Inaddition, plasticizers, deodorants and antioxidants can be added inaccordance with practices well known in the art.

The following examples serve to illustrate the invention but are notintended as limitations. All percentages used in the examples are byweight unless otherwise indicated.

EXAMPLE 1 A flexible polyurethane foam was prepared from the followingingredients.

Ingredient: Grams Polyalkyleneether triol" 100 Tolylene diisocyanate 45Silicone oil 0.8 Dibutyltin dilaurate 0.1 N-ethylmorpholine 0. 1 1,3-bis(dimethylamino )-2- propanol 0.16 Water 3.5

"A polyoxypropylene derivative of glycerine having a basic functionalityof 3, an average molecular weight of about 3,000, and a hydroxyl numberof about 56.

A mixture of 52.8 percent 2,4-tolylene diisocyanate, 18.2 percent2,6-tolylene diisocyanate and 29.0 percent 2,5-tolylene diisocyanate. Apolysiloxane polyoxyalkylene block copolymer used as a foam stabilizeror surfactant available commercially under the trade designationSilicone L540" from the Union Carbide Corporation.

In this example, all of the ingredients except the tolylene diisocyanatewere first blended together in a laboratory blender. The tolylenediisocyanate was then added as rapidly as possible and blendedthoroughly. The mixture was poured into an open 3-inch X 6.5-inch XlO-inch cardboard box. The resulting flexible foam was allowed to standfor about 15 minutes at room temperature and then was cured at 120 C.for 30 minutes. It was then allowed to stand overnight at roomtemperature. The density of the foam was 1.81 p.c.f.; it was classifiedas burning according to ASTM test D1692, with a burning rate of 2.96inches per minute.

EXAMPLE 2 A flexible polyurethane foam was prepared as described inExample 1 with the exception that the tolylene diisocyanate mixture ofExample 1 was replaced with 45 grams of a mixture of percent 2,4-tolylene diisocyanate and 20 percent 2,6-tolylene diisocyanate. Thedensity of the resulting foam was 1.81 p.c.f.; it was classified asburning according to ASTM test D1692, with a burning rate of 4.27 inchesper minute. Comparison of this result with that of Example 1 shows thatthe foam of this example burned 30.7 percent faster than the foam ofExample 1.

EXAMPLE 3 A flexible polyurethane foam was prepared as described inExample 1, with the exceptions that the polyalkyleneether triol ofExample 1 was replaced with grams of a polyalkyleneether triol having amolecular weight of about 3,500 and a hydroxyl number of about 47.5(known under the trade designation of Niax polyol 16-46), and thetolylene diisocyanate component of Example 1 was replaced with 42 gramsof a mixture of 64.8 percent 2,4-tolylene diisocyanate, 18.2 percent2,6-tolylene diisocyanate, and 17.0 percent of 2,5-tolylenediisocyanate. The density of the resulting foam was 1.81 p.c.f.; it wasclassified as burning according to ASTM test D1692, with a burning rateof 3.38 inches per minute.

EXAMPLE 4 A flexible polyurethane foam was prepared as described inExample 3 with the exception that the tolylene diisocyanate mixture ofExample 2 was replaced with 42 grams of a mixture of 52.8 percent2,4-tolylene diisocyanate, 18.2 percent 2,6-tolylene diisocyanate, and29.0 percent 2,5-to1ylene diisocyanate. The density of the resultingfoam was 1.97 p.c.f.; it was classified as burning according to ASTMtest D1692, with a burning rate of 2.60 inches per minute.

EXAMPLE 5 A flexible polyurethane foam was prepared as described inExample 3 with the exception that the tolylene diisocyanate mixture ofExample 3 was replaced with 42 grams of a mixture of 32.5 percent2,4-to1y1ene diisocyanate, 17.5 percent 2,6-toly1ene diisocyanate, and50.0 percent 2,5-tolylene diisocyanate. The density of the resultingfoam was 2.63 p.c.f.; it was classified as burning according to ASTMtest D1692, with a burning rate of 3.21 inches per minute. The body ofthe foam actually burned significantly slower than this; surface flashaccounted for the rate of 3.21 inches per minute.

EXAMPLE 6 A flexible polyurethane foam was prepared as described inExample 3 with the exception that the tolylene diisocyanate mixture ofExample 3 was replaced with 42 grams of a mixture of 80 percent 2,4-tolylene diisocyanate and 20 percent 2,6-tolylene diisocyanate. Thedensity of the resulting foam was 2.08 p.c.f.; it was classified asburning according to ASTM test D1692, with a burning rate of 4.70 inchesper minute. Comparison of this result with those of Examples 3 to 5shows that the foam of this example burned 28.1 percent faster than thefoam of Example 3, 44.7 percent faster than the foam of Example 4, and31.7 percent faster than the foam of Example 5.

EXAMPLE 7 A flexible polyurethane foam was prepared as described inExample 4 with the exception that 10.0 grams of a flame-retardingmaterial, 2,2- bis(chloromethyl)-1,3-propylenebis[bis(2-chloroethyl)phosphate], commercially available as Phosgard 2XC-20" fromthe Monsanto Company, was added to the formulation. The density of theresulting foam was 2.12 p.c.f. Of six samples tested according to ASTMD1692, five were self-extinguishing with an extent of burning of 4.56inches, and one burned with a burning rate of 1.94 inches per minute.

EXAMPLE 8 Example 7 was repeated, except that 11.0 grams of Phosgard2XC-20 were employed. The formulation resulted in a flexible foam havinga density of 2.13 p.c.f. All samples tested were self-extinguishing,with an extent of burning of 3.75 inches.

EXAMPLE 9 EXAMPLE 10 Example 9 was repeated, except that 13.0 grams ofPhosgard 2XC-20 were employed. The formulation resulted in a flexiblefoam having a density of 2.10 p.c.f. It was classified asself-extinguishing according to ASTM D1692, with an extent of burning of2.65 inches. Comparison of the results of Examples 9 and 10 with thoseof Examples 7 and 8 shows that less of the flame-retarding phosphateester is required to achieve a self-extinguishing rating for the foamsof Examples 7 and 8 than for the foams of Examples 9 and 10.

EXAMPLE 1 1 A rigid polyurethane foam was prepared from the followingingredients.

Ingredient: Grams Polyether polyol" 1 15.6 Polyisocyanate 73.4 Tolylenediisocyanate 43.5 Silicone oil 2.0 N,N',N, N'-tetramethylbutane-1 ,4-

diamine 1.5 Flurotrichloromethane 45 "A polyoxypropylene derivative ofsucrose having an equivalent weight of about 1 16 and a hydroxyl numberof about 485.

A polymethylene polyphenylisocyanate having an isocyanate equivalent ofabout 133.5, an available NCO content of about 32 percent and aviscosity of 25C. of about 250 c.p.s.

"A mixture of 52.8 percent 2,4-to1ylene diisocyanate, 18.2 percent2,6-tolylene diisocyanate, and 29.0 percent 2,5-toly1ene diisocyanate. Apolysiloxane polyoxyalkylene block copolymer used as a foam stabilizeror surfactant, available commercially under the trade designationDC-195" from the Dow Corning Corporation.

EXAMPLE 12 A rigid polyurethane foam was prepared as described inExample 11, with the exception that the tolylene diisocyanate mixture ofExample 11 was replaced with 43.5 grams of a mixture of percent2,4-to1y1ene diisocyanate and 20 percent 2,6-tolylene diisocyanate. Thedensity of the resulting foam was 1.51 p.c.f.; it was classified asburning according to ASTM D1692, with a burning rate of 17.49 inches perminute. Comparison of this result with that of Example 11 shows that thefoam of this example burns 35.2 percent faster than the foam of Example1 1.

In like manner, polyurethane foams are made less flammable by replacinga portion of the isocyanate component conventionally employed,particularly 2,4- and/or 2,6-tolylene diisocyanate, in producingpolyurethane foams by mono-, dior trichloroor bromo, ring-substituted2,5-tolylene diisocyanates or mixtures thereof, provided that suchrepresent from about 8 percent to about 60 percent, preferably about 15to about 50 percent, of the total isocyanate component used to make thefoam.

Although specific examples of the invention have been set forthhereinabove, it is not intended to limit the invention thereto, but toinclude all of the variations and modifications falling within the scopeof the appended claims.

We claim:

1. A fire-retardant polyurethane foam comprising the reaction product ofan aromatic polyisocyanate mixture comprising from about 8 to about 60weight percent based on the total polyisocyanate mixture of 2,5-tolylenediisocyanate, a ring-substituted chloroor bromo-derivative of2,5-tolylene diisocyanate, or mixtures thereof and a polyol having atleast two active hydrogens selected from polyether polyols, polyesterpolyols and mixtures thereof in the presence of a foaming agent.

2. A fire-retardant polyurethane foam in accordance with claim 1 inwhich the polyisocyanate mixture comprises from about 40 to about 92percent 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate or mixturesthereof.

3. A fire-retardant polyurethane foam in accordance with claim 2 inwhich the polyisocyanate mixture comprises from about 15 to about 50percent 2,5-tolylene diisocyanate.

4. A fire-retardant polyurethane foam in accordance with claim 1comprising a minor quantity of a flammability retarding additivecomposition.

5. A fire-retardant polyurethane foam in accordance with claim 4 inwhich the polyisocyanate mixture comprises from about 40 to about 92percent 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate or mixturesthereof.

2. A fire-retardant polyurethane foam in accordance with claim 1 inwhich the polyisocyanate mixture comprises from about 40 to about 92percent 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate or mixturesthereof.
 3. A fire-retardant polyurethane foam in accordance with claim2 in which the polyisocyanate mixture comprises from about 15 to about50 percent 2,5-tolylene diisocyanate.
 4. A fire-retardant polyurethanefoam in accordance with claim 1 comprising a minor quantity of aflammability retarding additive composition.
 5. A fire-retardantpolyurethane foam in accordance with claim 4 in which the polyisocyanatemixture comprises from about 40 to about 92 percent 2,4-tolylenediisocyanate, 2,6-tolylene diisocyanate or mixtures thereof.